Rapid manufacturing of porous metal prostheses

ABSTRACT

An orthopaedic prosthesis and a method for rapidly manufacturing the same are provided. The orthopaedic prosthesis includes a solid bearing layer, a porous bone-ingrowth layer, and an interdigitating layer therebetween. A laser sintering technique is performed to manufacture the orthopaedic prosthesis.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional PatentApplication Ser. No. 61/507,151, filed Jul. 13, 2011, the disclosure ofwhich is hereby expressly incorporated by reference herein in itsentirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to porous metal prostheses. Moreparticularly, the present disclosure relates to rapid manufacturing ofporous metal prostheses.

BACKGROUND OF THE DISCLOSURE

Orthopaedic prostheses are commonly used to replace at least a portionof a patient's bone following traumatic injury or deterioration due toaging, illness, or disease, for example.

When the orthopaedic prosthesis is implanted into a joint, theorthopaedic prosthesis may be configured to articulate with an adjacentorthopaedic component. For example, when the orthopaedic prosthesis isimplanted into the patient's hip joint, the orthopaedic prosthesis maybe socket-shaped to receive and articulate with an adjacent femoralcomponent.

The orthopaedic prosthesis may be at least partially porous to promoteingrowth of the patient's surrounding bone and/or soft tissue, which mayenhance the fixation between the orthopaedic prosthesis and thepatient's surrounding bone and/or soft tissue. Typically, the porousportion of the orthopaedic prosthesis is attached to a solid component,such as by diffusion bonding. Diffusion bonding, however, requires asignificant amount of time to complete and subjects the orthopaedicprosthesis to high temperatures.

SUMMARY

The present disclosure provides an orthopaedic prosthesis having a solidbearing layer, a porous bone-ingrowth layer, and an interdigitatinglayer therebetween. The present disclosure also provides a method forrapidly manufacturing the orthopaedic prosthesis, such as by performinga laser sintering process.

According to an embodiment of the present disclosure, a method isprovided for rapidly manufacturing an orthopaedic prosthesis. Theorthopaedic prosthesis has a porous substrate, the porous substrateincluding an outer surface and a plurality of ligaments that definepores beneath the outer surface. The method includes the steps of:depositing a plurality of metal powder particles onto the outer surfaceof the porous substrate; allowing at least a first portion of theplurality of metal powder particles to enter the pores beneath the outersurface of the porous substrate, the first portion of the plurality ofmetal powder particles being sized to fit within the pores of the poroussubstrate; and applying an energy source to the first portion of theplurality of metal powder particles to form solid metal, the solid metalinterdigitating into the pores of the porous substrate.

According to another embodiment of the present disclosure, a method isprovided for rapidly manufacturing an orthopaedic prosthesis. Theorthopaedic prosthesis has a solid metal component and a porous metalcomponent, the porous metal component including a plurality of ligamentsthat define pores. The method includes the steps of: depositing aplurality of metal powder particles into the pores of the porous metalcomponent; and directing an energy source into the pores of the porousmetal component to convert the plurality of metal powder particles inthe pores to solid metal in the pores, the solid metal in the porescoupling the solid metal component to the porous metal component.

According to yet another embodiment of the present disclosure, anorthopaedic prosthesis is provided including a solid metal layer havinga first thickness, a porous metal layer having a second thickness thatis less than or equal to the first thickness, the porous metal layerincluding a plurality of ligaments that define pores, and aninterdigitating layer having a third thickness, the interdigitatinglayer including a plurality of ligaments that define pores, the pores ofthe interdigitating layer being substantially filled with solid metal,the interdigitating layer extending between the solid metal layer andthe porous metal layer to couple the solid metal layer to the porousmetal layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of thisdisclosure, and the manner of attaining them, will become more apparentand the invention itself will be better understood by reference to thefollowing description of embodiments of the invention taken inconjunction with the accompanying drawings, wherein:

FIG. 1 is a flow chart of an exemplary method for rapidly manufacturingan orthopaedic prosthesis;

FIG. 2 is a schematic diagram of a porous substrate located within abuild chamber;

FIG. 3 is another schematic diagram showing a first layer of metalpowder deposited into the porous substrate of FIG. 2;

FIG. 4 is another schematic diagram showing a laser selectivelyconverting the first layer of metal powder of FIG. 3 to solid metal;

FIG. 5 is another schematic diagram showing a second layer of metalpowder deposited into the porous substrate of FIG. 4;

FIG. 6 is another schematic diagram showing the laser selectivelyconverting the second layer of metal powder of FIG. 5 to solid metal;

FIG. 7 is another schematic diagram showing a third layer of metalpowder deposited into and atop the porous substrate of FIG. 6;

FIG. 8 is another schematic diagram showing the laser selectivelyconverting the third layer of metal powder of FIG. 7 to solid metal;

FIGS. 9-11 are schematic diagrams similar to FIG. 8, further showing thelaser selectively converting additional layers of metal powder to solidmetal to produce an orthopaedic prosthesis;

FIG. 12 is a schematic diagram of the orthopaedic prosthesis of FIG. 11,further including an exploded polymeric liner, and

FIG. 13 is a schematic diagram of another, patient-specific orthopaedicprosthesis shown implanted in a patient's bone.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate exemplary embodiments of the invention and suchexemplifications are not to be construed as limiting the scope of theinvention in any manner.

DETAILED DESCRIPTION

FIG. 1 provides an exemplary method 100 for designing and manufacturingan orthopaedic prosthesis. Method 100 is exemplified with reference toFIGS. 2-7.

Beginning at step 102 of method 100 (FIG. 1), a porous substrate 200 isprovided having a large plurality of struts or ligaments 202 that defineopen spaces or pores 204 therebetween, as shown in FIG. 2. Ligaments 202may be constructed, at least in part, of a first biocompatible metal,such as tantalum, a tantalum alloy, niobium, a niobium alloy, or anothersuitable metal, for example. In an exemplary porous substrate 200, pores204 between ligaments 202 form a matrix of continuous channels having nodead ends, such that growth of cancellous bone and/or soft tissuethrough porous substrate 200 is uninhibited. Thus, porous substrate 200may provide a matrix into which cancellous bone and/or soft tissue maygrow to provide fixation of porous substrate 200 to the patient's bone.

According to an exemplary embodiment of the present disclosure, poroussubstrate 200 is a highly porous biomaterial having a porosity as low as55%, 65%, or 75% or as high as 80%, 85%, or 90%. An example of such amaterial is produced using Trabecular Metal™ Technology generallyavailable from Zimmer, Inc., of Warsaw, Ind. Trabecular Metal™ is atrademark of Zimmer, Inc. Porous substrate 200 may be formed from areticulated vitreous carbon foam substrate which is infiltrated andcoated with the above-described first biocompatible metal (e.g.,tantalum) by a chemical vapor deposition (“CVD”) process in the mannerdisclosed in detail in U.S. Pat. No. 5,282,861 to Kaplan, entitled “OpenCell Tantalum Structures for Cancellous Bone Implants and Cell andTissue Receptors,” filed Mar. 11, 1992, the entire disclosure of whichis expressly incorporated herein by reference. By performing this CVDprocess, each ligament 202 of porous substrate 200 includes a carboncore covered by a thin film of the first biocompatible metal (e.g.,tantalum). It is also within the scope of the present disclosure thatporous substrate 200 may be in the form of a fiber metal pad, forexample, the ligaments of the fiber metal pad being constructed entirelyor substantially entirely of the first biocompatible metal.

Porous substrate 200 may be fabricated to virtually any desired porosityand pore size in order to selectively tailor porous substrate 200 for aparticular application, as discussed in the above-incorporated U.S. Pat.No. 5,282,861. In an exemplary embodiment, porous substrate 200 has anaverage pore size between 100 micrometers and 1,000 micrometers, andmore specifically about 500 micrometers.

During the providing step 102 of method 100 (FIG. 1), porous substrate200 may be in a desired shape and size that is suitable for implantationin a patient's body. For example, the illustrative porous substrate 200of FIG. 2 is provided in a hollow hemispherical shape and in a size thatis suitable for implantation as an acetabular shell in a patient's hipjoint. However, it is also within the scope of the present disclosurethat porous substrate 200 may require subsequent shaping or machiningafter the providing step 102 of method 100 (FIG. 1) and before beingimplanted in the patient's body. Although the illustrative poroussubstrate 200 of FIG. 2 is shaped and sized for use as an acetabularshell in the patient's hip joint, it is also within the scope of thepresent disclosure that the porous substrate may be shaped and sized foruse as a femoral component, a tibial component, a humeral component, aspinal component, a dental component, or another orthopaedic component,for example.

Porous substrate 200 includes a first, bone-engaging surface 206 thatinteracts with the patient's bone. In the illustrated embodiment of FIG.2, the bone-engaging surface 206 of porous substrate 200 is a regular,stock surface that is shaped to interact with a prepared (e.g., reamed,cut, etc.) bone surface of a patient. In the illustrated embodiment ofFIG. 13, on the other hand, the bone-engaging surface 206′ of poroussubstrate 200′ is a patient-specific surface that is shaped assubstantially a negative of the particular patient's bone surface S toconform to the particular patient's bone surface S, even withoutpreparing (e.g., reaming, cutting, etc.) the patient's bone B. Thepatient-specific bone-engaging surface 206′ may be designed to be highlyirregular, arbitrary, non-parametric, or biologically complex in shapeto fill a void or defect in the particular patient's bone B and toaccommodate the surrounding anatomy of the particular patient. Anexemplary method of manufacturing such a patient-specific component isdescribed in U.S. patent application Ser. No. 13/464,069 to Li et al.,entitled “Patient-Specific Manufacturing of Porous Metal Prostheses,”filed May 4, 2012, the entire disclosure of which is expresslyincorporated herein by reference.

Porous substrate 200 also includes a second, solid-receiving surface208. In the illustrated embodiment of FIG. 2, solid-receiving surface208 is concave in shape and opposes bone-engaging surface 206 of poroussubstrate 200.

Continuing to step 104 of method 100 (FIG. 1), porous substrate 200 isplaced inside a build chamber 300, as shown in FIG. 2. Build chamber 300may be evacuated and flushed with an inert gas (e.g., argon) to avoidoxidation. Build chamber 300 may also be heated to improve theefficiency of the remaining process steps.

Next, in step 106 of method 100 (FIG. 1), a first layer of metal powder302 is deposited onto porous substrate 200 in build chamber 300, asshown in FIG. 3. More specifically, the first layer of metal powder 302is deposited onto solid-receiving surface 208 of porous substrate 200.Additionally, the first layer of metal powder 302 may be depositedaround porous substrate 200 to support and stabilize porous substrate200 in build chamber 300. In an exemplary embodiment, the first layer ofmetal powder 302, and each subsequent layer, is about 20 micrometers toabout 30 micrometers thick. After depositing each new layer of metalpowder 302 into build chamber 300, the newly deposited layer may beleveled by rolling a roller (not shown) across build chamber 300, byvibrating build chamber 300, or by another suitable leveling technique.

According to an exemplary embodiment of the present disclosure, metalpowder 302 comprises a second biocompatible metal that differs from thefirst biocompatible metal of porous substrate 200. For example, ifligaments 202 of porous substrate 200 comprise or are coated withtantalum, particles 304 of metal powder 302 may comprise titanium or atitanium alloy (e.g., Ti-6Al-4V).

According to another exemplary embodiment of the present disclosure,particles 304 of metal powder 302 are sized smaller than pores 204 ofporous substrate 200. Particles 304 of metal powder 302 may be less thanabout 10% the size of pores 204 of porous substrate 200. Morespecifically, particles 304 of metal powder 302 may be as little asabout 1%, about 2%, or about 3% the size of pores 204 of poroussubstrate 200 and as much as about 4%, about 5%, or about 6% the size ofpores 204 of porous substrate 200, or within a range defined between anypair of the foregoing values. For example, if pores 204 of poroussubstrate 200 are about 500 micrometers in size, each particle 304 ofmetal powder 302 may be as small as about 5 micrometers, 10 micrometers,or 15 micrometers in size and as large as about 20 micrometers, 25micrometers, or 30 micrometers in size. In this embodiment, a largenumber of particles 304 may fall into pores 204 of porous substrate 200,especially pores 204 that are exposed along solid-receiving surface 208of porous substrate 200, as shown in FIG. 3. The above-describedleveling techniques may also encourage particles 304 to fall into pores204 of porous substrate 200.

After the depositing step 106 of method 100, select areas of metalpowder 302 are exposed to an energy source during step 108 of method 100(FIG. 1). The applied energy source causes localized sintering ormelting of particles 304 of metal powder 302, which converts selectareas of metal powder 302 to solid metal 306. Each newly-formed regionof solid metal 306 may bond to a previously-formed region of solid metal306 and to porous substrate 200, as shown in FIG. 4. In this manner,solid metal 306 is selectively and rapidly formed upon porous substrate200 while simultaneously bonding solid metal 306 to porous substrate200.

In an exemplary embodiment, the applying step 108 of method 100 (FIG. 1)involves a direct metal laser sintering (DMLS) process, where the energysource is a focused, high-powered laser 400 (e.g., a ytterbium fiberoptic laser). The DMLS process may also be referred to as a selectivelaser sintering (SLS) process or a selective laser melting (SLM)process. Suitable DMLS systems are commercially available from 3DSystems, Inc., of Rock Hill, S.C.

Laser 400 may be controlled using a suitable computer processor having,for example, computer-aided design (CAD) software and/or computer-aidedmanufacturing (CAM) software installed thereon. Such software can beused to rapidly create computer numerical control (CNC) code that willcontrol each individual pass of laser 400 across build chamber 300. Forexample, as each layer of metal powder 302 is deposited into buildchamber 300 (i.e., along the z-axis), the CNC code may direct laser 400side-to-side across build chamber 300 (i.e., along the y-axis) andback-and-forth across build chamber 300 (i.e., along the x-axis). Toconvert select areas of metal powder 302 to solid metal 306, laser 400may be activated at select xy-coordinates. To leave other areas of metalpowder 302 as is, without forming solid metal 306, laser 400 may bedeactivated at other xy-coordinates or may avoid traveling to thosexy-coordinates altogether.

As shown by comparing FIGS. 3 and 4, even particles 304 of metal powder302 that settled into pores 204 of porous substrate 200 during thedepositing step 106 of method 100 (FIG. 1) may be converted to solidmetal 306 during the applying step 108 of method 100 (FIG. 1). Accordingto an exemplary embodiment of the present disclosure, the secondbiocompatible metal of particles 304 of metal powder 302 has a lowermelting point than the first biocompatible metal of ligaments 202 ofporous substrate 200. For example, if ligaments 202 of porous substrate200 comprise or are coated with tantalum, which has a melting pointabove 3,000° C., particles 304 of metal powder 302 may comprise titaniumor a titanium alloy (e.g., Ti-6Al-4V), which have melting points below1,700° C. In this embodiment, even when laser 400 passes over and isabsorbed by porous substrate 200, as shown in FIG. 4, thethermally-stable ligaments 202 of porous substrate 200 remainsubstantially intact without sintering or melting. However, when laser400 passes over and is absorbed by particles 304 of metal powder 302,particles 304 may sinter or melt to form solid metal 306. If the meltingpoints between the first and second biocompatible metals aresufficiently different, solid metal 306 within each pore 204 of poroussubstrate 200 may be able to maintain substantially the same elementalcontent as metal powder 302, without incorporating material from thethermally-stable ligaments 202 of porous substrate 200.

As shown in FIGS. 5-11, the depositing step 106 and the applying step108 of method 100 (FIG. 1) are repeated until solid metal 306 reaches afinal, desired shape. As more metal powder 302 is deposited atop thepreviously-formed regions of solid metal 306, particles 304 of metalpowder 302 begin to substantially fill the exposed pores 204 of poroussubstrate 200, as shown in FIG. 5. As even more metal powder 302 isdeposited atop the previously-formed regions of solid metal 306,particles 304 of metal powder 302 begin to accumulate atopsolid-receiving surface 208 of porous substrate 200, as shown in FIGS.7-11. After each new layer of metal powder 302 is deposited, selectareas of the newly-deposited layer are exposed to laser 400, convertingmore metal powder 302 to solid metal 306.

Together, porous substrate 200 and solid metal 306 form orthopaedicprosthesis 500 that is suitable for implantation in a patient's body.For example, the illustrative orthopaedic prosthesis 500 of FIG. 12 issuitable for implantation as an acetabular cup in a patient's hip joint.Although the illustrative orthopaedic prosthesis 500 of FIG. 12 issuitable for implantation as an acetabular cup in the patient's hipjoint, it is also within the scope of the present disclosure that theorthopaedic prosthesis may be configured for implantation in a patient'sfemur, tibia, humerus, spine, or mouth, for example.

Returning to FIG. 6, porous substrate 200 and solid metal 306 cooperateto define an interdigitating layer L₁ beneath the solid-receivingsurface 208 of porous substrate 200. Within the interdigitating layerL₁, solid metal 306 metallurgically and/or mechanically interacts withligaments 202 of porous substrate 200 to create a strong attachmentbetween solid metal 306 and porous substrate 200. The interdigitatinglayer L₁ may have a thickness of approximately 250 micrometers or more,500 micrometers or more, 1,000 micrometers (1 millimeter) or more, or1,500 micrometers (1.5 millimeters) or more, for example. Solid metal306 in the interdigitating layer L₁ may be formed from particles 304 ofmetal powder 302 that settled into pores 204 of porous substrate 200before exposure to laser 400, as shown in FIGS. 3-6. Additionally, solidmetal 306 in the interdigitating layer L₁ may be formed from particles304 of metal powder 302 that settled atop solid-receiving surface 208 ofporous substrate 200 before exposure to laser 400, but that latersettled into pores 204 of porous substrate 200 upon exposure to laser400. Depending on the size of pores 204, the size of particles 304,and/or the degree to which particles 304 are heated and renderedflowable, solid metal 306 may substantially or completely fill pores 204in the interdigitating layer L₁ of porous substrate 200.

In addition to the above-described interdigitating layer L₁, orthopaedicprosthesis 500 further includes a solid bearing layer L₂ and a porousbone-ingrowth layer L₃, as shown in FIG. 12. Solid metal 306 extendsbeyond porous substrate 200 and the interdigitating layer L₁ to form thesolid bearing layer L₂. The solid bearing layer L₂ may have a thicknessof approximately 0.5 inch or more, 1.0 inch or more, 1.5 inches or more,or 2.0 inches or more, for example. Porous substrate 200 extends beyondsolid metal 306 and the interdigitating layer L₁ to define the porousbone-ingrowth layer L₃.

An exemplary orthopaedic prosthesis 500 is predominantly solid, notporous, by weight and/or volume. In one embodiment, the thickness of theporous bone-ingrowth layer L₃ is less than or equal to the thickness ofthe solid bearing layer L₂ to arrive at orthopaedic prosthesis 500 thatis predominantly solid. In this exemplary embodiment, the solid bearinglayer L₂ of orthopaedic prosthesis 500 constitutes more than just a thinsurface coating on the porous bone-ingrowth layer L₃.

Advantageously, the above-described depositing step 106 and theabove-described applying step 108 of method 100 (FIG. 1) produceorthopaedic prosthesis 500 in a rapid and automated manner. The solidbearing layer L₂ of orthopaedic prosthesis 500 may be rapidly andautomatically manufactured to strengthen and support orthopaedicprosthesis 500 and/or to interact with an adjacent orthopaediccomponent. In the illustrated embodiment of FIG. 12, for example, thesolid bearing layer L₂ of orthopaedic prosthesis 500 is configured toreceive a polymeric liner 502, which in turn interacts with and receivesthe patient's adjacent femoral head. Also, the solid bearing layer L₂ oforthopaedic prosthesis 500 may be rapidly and automatically manufacturedin a highly complex geometry, without requiring any subsequent shaping.At substantially the same time, the interdigitating layer L₁ may berapidly and automatically produced to bond the solid bearing layer L₂ tothe underlying porous bone-ingrowth layer L₃.

Continuing to step 110 of method 100 (FIG. 1), orthopaedic prosthesis500 is removed from build chamber 300, leaving behind metal powder 302that was not converted to solid metal 306. Also, excess metal powder 302may be removed from porous substrate 200 by shaking orthopaedicprosthesis 500 and/or by blowing pressurized air into porous substrate200, for example. Orthopaedic prosthesis 500 may then be subjected toany necessary cleaning, shaping, processing, sterilizing, or packagingsteps. For example, in the illustrated embodiment of FIG. 12, thepolymeric liner 502 may be coupled to solid bearing layer L₂ oforthopaedic prosthesis 500 to facilitate articulation with the patient'sadjacent femoral head.

Finally, in step 112 of method 100 (FIG. 1), orthopaedic prosthesis 500is implanted into the patient's body. Bone-engaging surface 206 oforthopaedic prosthesis 500 is implanted against the patient's bone toencourage bone and/or soft tissue ingrowth into the porous bone-ingrowthlayer L₃ of orthopaedic prosthesis 500. Orthopaedic prosthesis 500 maybe secured in place using suitable fasteners (e.g., bone screws) or bonecement, for example.

While this invention has been described as having exemplary designs, thepresent invention can be further modified within the spirit and scope ofthis disclosure. This application is therefore intended to cover anyvariations, uses, or adaptations of the invention using its generalprinciples. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

What is claimed is:
 1. A method of rapidly manufacturing an orthopaedicprosthesis having a porous substrate, the porous substrate including anouter surface and a plurality of ligaments that define pores beneath theouter surface, the method comprising the steps of: depositing aplurality of metal powder particles onto the outer surface of the poroussubstrate; allowing at least a first portion of the plurality of metalpowder particles to enter the pores beneath the outer surface of theporous substrate, the first portion of the plurality of metal powderparticles being sized to fit within the pores of the porous substrate;and applying an energy source to the first portion of the plurality ofmetal powder particles to form solid metal, the solid metalinterdigitating into the pores of the porous substrate.